This invention is generally directed to toner compositions and developer compositions, and the use of these compositions in electrostatographic imaging systems including color imaging processes. More specifically, the present invention is directed to toner compositions containing therein ionic dyes bound to ionophoric or ionomeric polymers. These ion binding segments are effective in incorporating salts and ionic dyes into dielectric resins and cause the toner particles to assume a positive or negative triboelectric charge. The resulting toners are non-toxic and are thermally and photochemically stable. The toner and developer compositions of the present invention are particularly useful in electrostatographic imaging systems and in colored imaging processes.
Electrostatographic processes are well known in the art. For example, U.S. Pat. No. 4,592,989 discloses an electrostatic toner composition comprised of resin particles, pigment particles and a complex of a dipolar molecule or salt attached to an ionophoric polymer, and a method for using such toner compositions in electrostatographic processes.
Use of ionophoric and ionomeric resins in toner and developer compositions has not met with extensive applications. However, use of such resins in toner and developer compositions is known in the art. For example, U.S. Pat. No. 4,592,989, described above, discloses ionophoric polymers as charge enhancing additives. U.S. Pat. No. 5,314,778 discloses ionomeric polymers, optionally complexed to a Lewis acid, a salt, or an ion thereof, as charge enhancing additives in toner compositions. U.S. Pat. No. 4,925,673 discloses a toner composition comprising a colorant synthesized from a pigment component, an ionomeric resin and, optionally, a humic acid component. However, the dyes and pigments are covalent in their bonding nature, and therefore do not interact with the ionomeric polymer in the way that ionic dyes would interact.
A recognized problem in prior art toner and developer compositions is that high quality color images require that toner colorants be pigments of colloidal dimensions, or dyes solubilized in the toner resin. However, reduction of pigments to colloidal dimensions usually requires special milling and grinding operations, coupled with flushing processes. Resin-soluble dyes are an alternative approach; however, such dyes are generally less stable than pigments, and dye-based images tend to degrade rapidly when exposed to ambient conditions in most office environments. Generally, such resin-soluble dyes are less stable than pigments in their environmental, thermal and photochemical characteristics. A need therefore continues to exist to provide better methods for incorporating colorants into toner compositions, or to provide more stable dyes that degrade less rapidly.
One approach to increase the stability and usefulness of soluble dyes has been utilized in the area of silver halide photography. In that art, dyes are typically bound to polymers and mordants to enhance the heat, light and environmental stability of the dyes. Here, mordant refers to a chemical used for fixing colors on textiles by absorption. For example, mordants may include soluble salts of aluminum, chromium, iron, tin and antimony. The dyes are often then "laked" with salts or substances such as phosphotungstic or phosphomolybdic acid to render them insoluble and stable. Here, laking refers to interacting a soluble dye with a precipitant and an absorptive substrate, typically resulting in a pigment-type composition.
A further recognized problem with pigments and dyes is that such pigments and dyes tend to have a dominant effect on the charging characteristics of a toner or developer composition. Therefore, the charging characteristics, such as triboelectric charging, of a toner or developer composition varies depending on the specific pigments or dyes incorporated therein. Thus, even a slight change in the color component of a toner or developer composition alters the charging characteristics and requires that the charging components be redesigned. Accordingly, there exists a continued need for improved toner and developer compositions with charging characteristics that are less dependent upon the specific pigments or dyes incorporated therein.